As the essential technology of human-robotics interactive wearable devices, the robotic knee prosthesis can provide above-knee amputations with functional knee compensations to realize their physical and psychological social regression. With the development of mechanical and mechatronic science and technology, the fully active knee prosthesis that can provide subjects with actuating torques has demonstrated a better wearing performance in slope walking and stair ascent when compared with the passive and the semi-active ones. Additionally, with intelligent human-robotics control strategies and algorithms, the wearing effect of the knee prosthesis has been greatly enhanced in terms of stance stability and swing mobility. Therefore, to help readers to obtain an overview of recent progress in robotic knee prosthesis, this paper systematically categorized knee prostheses according to their integrated functions and introduced related research in the past ten years (2010–2020) regarding (1) mechanical design, including uniaxial, four-bar, and multi-bar knee structures, (2) actuating technology, including rigid and elastic actuation, and (3) control method, including mode identification, motion prediction, and automatic control. Quantitative and qualitative analysis and comparison of robotic knee prosthesis-related techniques are conducted. The development trends are concluded as follows: (1) bionic and lightweight structures with better mechanical performance, (2) bionic elastic actuation with energy-saving effect, (3) artificial intelligence-based bionic prosthetic control. Besides, challenges and innovative insights of customized lightweight bionic knee joint structure, highly efficient compact bionic actuation, and personalized daily multi-mode gait adaptation are also discussed in-depth to facilitate the future development of the robotic knee prosthesis.
To accurately simulate the plasma arc (PA) behavior in a wide current range, a steady two-dimensional model for the numerical calculation of the axisymmetric PA considering the high temperature cathode region (HTCR) was proposed. Based on the experimentally measured HTCR area, two distribution forms, namely, the mean value method and the Gaussian distribution method, were used to simulate the current density distribution behavior in the tungsten tip. The two proposed current densities were compared with the average current density model with a fixed discharge region. The Gaussian distribution form was chosen after a comprehensive comparison of experimental measured data and simulation data in aspects of arc pressure, electron temperature, and arc voltage at a welding current of 120 A. The model was verified to be accepted in a current range of 110–170 A by comparing the simulated and measured peak arc pressure values. The model has higher prediction accuracy over the common plasma arc model with the unchanged tip cathode, extends the prediction current range, and provides a tool for optimizing the nozzle structure and process parameters.
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